Eb43-1

RGH Pharmacy E-Bulletin
Volume 43 (11): September 26, 2011

A joint initiative of the Patient Services Section and the Drug and Therapeutics Information Service of the Pharmacy Department, Repatriation General
Hospital, Daw Park, South Australia. The RGH Pharmacy E-Bulletin is distributed in electronic format on a weekly basis, and aims to present concise,
factual information on issues of current interest in therapeutics, drug safety and cost-effective use of medications.
Editor: Assoc. Prof. Chris Alderman, University of South Australia – Director of Pharmacy, RGH
Pharmacy Department, Repatriation General Hospital, Daw Park, South Australia 5041
Drug-induced photosensitivity reactions

Drug induced photosensitivity reactions are a relatively common side effect associated with many medications. These
reactions occur via activation of a chemical by ultra-violet or visible light. Many commonly used drugs are implicated
(both systemic and topical use), and include amiodarone, NSAIDs, phenothiazines, retinoids, quinolones, sulfonamides,
tetracyclines, and thiazides.
Most photosensitive reactions manifest as an exaggerated sunburn on areas of exposed skin; however, some phototoxic
reactions may cause a vesicular rash that resembles porphyria cutanea tardea (pseudoporphyria), or other skin conditions,
such as lichen planus. Some medications are associated with photosensitive reactions that result in discolouration of the
skin; for example, the characteristic blue-grey discolouration that can result from exposure to sunlight during amiodarone
treatment. A photosensitive rash to psoralens may resolve with a brown discolouration, and this reaction can be used
therapeutically for disorders such as vitiligo.
There are two main types of photosensitive reactions: phototoxic and photoallergic. Phototoxic reactions are the most
common form, which occur within minutes to hours after light exposure, and result from direct damage to the skin by a
photo-activated medication. The rash is confined to the area of sun exposure, and is dependent on the concentration of
drug and the amount of light exposure. Photoallergic reactions occur when repeated exposure to a photoactivated
medication results in a cell-mediated immune response. The rash usually occurs within 1–3 days after exposure.
Photoallergic reactions occasionally result in a rash that spreads beyond the boundary of light-exposed skin.
A medication history and history of light exposure should be elicited for patients presenting with a rash. Phototesting with
ultraviolet or visible light may be required for diagnosis, and also to determine whether the patient can tolerate lower
doses of the medication. Most photosensitive reactions are not severe; however, this is dependent on the concentration of
medication and the amount of light exposure. Usually, the reaction resolves after the medication is ceased, but this
depends on the severity of the reaction and the kinetics of the medication. Some patients develop a persistent light
reaction (or chronic actinic keratitis) where the condition persists after drug cessation and can be aggravated by minimal
exposure to UV light.
Before treatment with medications commonly associated with photosensitivity, patients should be counselled about the
potential for severe skin reactions after exposure to sunlight, and the importance of wearing protective clothing and
sunscreen. These measures may be adequate for patients who are required to take medications for a prolonged duration,
even after a reaction has occurred. If possible, however, the patient should avoid medication that has caused a skin
reaction. If a photoallergic reaction has occurred then the offending medications must be ceased, as reactions of
increasing severity may occur upon repeated exposure.


Acknowledgment – This E-Bulletin is based on work by Heather Forbes, Utility Pharmacist, RGH.

FOR FURTHER INFORMATION – CONTACT THE PHARMACY DEPARTMENT ON 82751763 or email: [email protected]
Information in this E-Bulletin is derived from critical analysis of available evidence – individual clinical circumstances should be considered
when making treatment decisions. You are welcome to forward this E-bulletin by email to others you might feel would be interested, or to print
the E-Bulletin for wider distribution. Reproduction of this material is permissible for purposes of individual study or research.

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Source: http://www.auspharmlist.net.au/ebulletin/vol43/eb43-11.pdf